Electro-optical analyzer for measuring percentage by weight of fat, protein and lactose in milk

ABSTRACT

Electro-optical apparatus for measurement of fat, protein, lactose and water or solids in milk wherein a milk sample is pumped by a homogenizer into an optical measurement cell. The specimen in the cell is then irradiated with reference and measurement beams at differing wavelengths for fat, protein, lactose and water respectively, and signals are stored indicative of uncorrected concentrations. A scaling and correction circuit includes cross-correction circuitry for compensating the effects on each reading caused by the other constituents. The signals so corrected are then provided in percentage by weight or weight over volume on suitable digital displays.

The present invention is directed to spectrophotometric analysis, andmore particularly to methods and apparatus for electro-optical analysisof emulsions and suspensions. Yet more specifically, the invention isdirected to methods and apparatus for infrared analysis of percentage byweight of fat, protein and lactose in milk.

An object of the present invention is to provide a spectrophotometricanalyzer for analysis of emulsions and suspensions which is economicalin manufacture, and which is reliable and accurate over extended periodsof operation. A further and more specific object of the invention is toprovide a compact electro-optical analyzer possessing a reduced numberof optical elements and a shortened beam path length as compared withprior art analyzers of similar type.

A further object of the invention is to provide an improved sample cellfor spectrophotometric analysis of fluids. Yet another object of theinvention is to provide an improved system and method for directingfluid to be analyzed to the sample cell.

In furtherance of the above, another object of the invention is toprovide an improved homogenizer for use in optical analysis of emulsionsand suspension such as milk.

The invention, together with additional objects, features and advantagesthereof, will be best understood from the following description, theappended claims and the accompanying drawings in which:

FIG. 1 is a top plan view of the optical portion of a presentlypreferred embodiment of the electro-optical analyzer provided inaccordance with the invention;

FIG. 2 is a schematic diagram of a system for directing fluid to beanalyzed to the sample cell in accordance with the presently preferredembodiment of the invention;

FIG. 3 is a functional block diagram of analysis electronics inaccordance with the invention;

FIG. 4 is a flow chart illustrating operation of the invention;

FIG. 5 is a side elevational view of the optical filter drum and codingdisc assembly illustrated in FIG. 1;

FIG. 6 is a side elevational view of the chopper disc and drive motorillustrated in FIG. 1;

FIG. 7 is a sectional view of the homogenizer in accordance with theinvention and illustrated schematically in FIG. 2;

FIG. 8 is an exploded perspective view of a presently preferredembodiment of the sample cell in accordance with the invention;

FIGS. 9, 10 and 11 are respective plan, side elevational and frontelevational views of the sample cell illustrated in FIG. 1 andschematically in FIG. 2;

FIGS. 12 and 13 are sectional views taken along the respective lines12--12 in FIG. 10 and 13--13 in FIG. 11; and

FIGS. 14a-14c together comprise an electrical schematic diagram of thememory, correction and scaling circuitry illustrated in block form inFIG. 3, FIGS. 14a and 14b being interconnected along the lines a-b ineach figure and FIGS. 14b and 14c being interconnected along the linesb-c in each figure.

The principles of invention will be described in detail in connectionwith a presently preferred application thereof to infraredspectrophotometric analysis of milk for percentage by weight of fat,protein, lactose and water or solids therein. However, it must berecognized that such principles are equally applicable to analysis ofother dairy products, to non-dairy food products such as meat and grain,and to non-food products such as paints, pharmaceuticals or chemical andgas compositions.

Referring to FIG. 1, the optical section or portion of theelectro-optical milk analyzer provided by the invention comprises aceramic infrared energy source 20 enclosed within its own coolingchamber 22. An interference filter 24 having a preferred pass band inthe range of three to ten microns is disposed in one wall of chamber 22and transmits infrared energy from source 20 to a pair of plane mirrors26,28 which operate to split the filtered infrared energy into divergingbeams 30,36 illustrated in phantom lines in FIG. 1. The first orreference beam 30 is reflected by plane mirror 26 onto the surface of aspherical mirror 32 from whence reference beam 30 is focused onto anoptical axis 34. The second or measurement beam 36 is reflected by planemirror 28 onto the surface of a second spherical mirror 38 from whencethe measurement beam is directed to intersect the reference beam from adirection orthogonal to beam axis 34. A sample cell generally indicatedat 66 and to be described in greater detail hereinafter in connectionwith FIGS. 8-13 is disposed at the focus of reference beam 30 on beamaxis 34. An ellipsoidal mirror 68 has a first focus at sample cell 66and a second focus at a detector 70 for directing and concentrating theoptical energy transmitted through sample cell 66 onto detector 70.Preferably, mirrors 26,28 32,38, 100 and 68 are of glass with highlyreflecting surfaces of aluminum or gold.

An upstanding vane or shutter 40 is disposed in the path of measurementor reference beam 36 or 30 (drawing shows vane in measurement beam), andis rotatably coupled to a motor 42 for a purpose to be describedhereinafter. A drive gear 44 is coupled to the shaft 46 of a servomotor48 through a slipping clutch mechanism (FIG. 1 and schematically in FIG.3) and through the idler gear 50 to a gear section 52 mounted to pivotin the plane of FIG. 1 about the pin 54. An arm 56 is rigidly coupled togear section 52 and has a comb or shutter 58 (FIGS. 1 and 3) carried onthe pivot-remote end thereof for adjustable placement within the path ofreference beam 30 between mirror 32 and sample cell 66 as controlled byservomotor 48. Comb 58 is arcuate in cross section with a radiuscentered on the axis of pivot pin 54 and, as best seen in FIG. 3,possesses a plurality of transversely spaced longitudinal slots 60 eachhaving a width which varies linearly with arcuate comb length. Thus,reference beam 30 is selectively attenuated as a linear function of thedegree or extent to which comb 58 is inserted into the beam. Comb 58 ispreferably coated with material which absorbs infrared energy. A coilspring 62 (FIG. 1) extends between arm 56 and a fixed stanchion 64 forresiliently biasing gear drive chain or transmission 44,50,52 so as toachieve substantially zero backlash. Coupled to gear 50 is an accuratelylinear potentiometer (schematically at 290 in FIG. 3) arranged toprovide a voltage to measuring circuits which is proportional to thepercentage transmission (%T) of the sample. A second potentiometer(schematically at 468 in FIG. 3) coupled to the same spindle within thesame potentiometer housing provides velocity feedback for the servomotordrive circuit.

A filter wheel 72 shown in FIGS. 1 and 5 comprises a drum coupled by thegears 74,76 to a drive motor 78 to rotate about a fixed axis 79 (FIG. 5)orthogonal to reference beam axis 34. Drum 72 includes segmentedcircumferential rim portions 80 which intersect reference beam 30between comb 58 and cell 66 as drum 72 is rotated, and an axially facingdisc portion 82 which intersects measurement beam 36. First and secondseries of optical absorption-type filters are respectively disposed inrim portion 80 and disc portion 82 of drum 72, and are grouped incoordinated pairs on corresponding radii from the axis of rotation 79such that one filter in each filter pair simultaneously intersectsassociated ones of the reference and measurement beams 30,36. Moreparticularly, four circumferentially spaced reference filters84,86,88,90 are mounted in associated segments of drum rim portion 80sequentially to intersect reference beam 30 as drum 72 is rotated in thecounterclockwise direction as viewed in FIG. 5. In analysis for fat,protein, lactose and water concentrations in milk, reference filters84-90 preferably possess nominal peak transmission wavelengths of 3.47,6.68, 7.67 and 5.55 microns respectively. A series of circumferentiallyspaced measurement filters 92,94,96 and 98 are disposed on the planardisc portion 82 of drum 72 in radially aligned association withrespective reference filters 84,86,88 and 90 as best seen in FIG. 5. Foranalysis of fat, protein, lactose and water in milk, filters 92,94,96and 98 preferably possess nominal peak transmission wavelengths of3.418, 6.46, 9.6 and 4.7 microns respectively. Preferably, at least fatmeasurement filter 84 is tiltably mounted (by means not shown) so as tofacilitate factory fine-tuning of the peak transmission wavelength tothe values indicated.

A detent locking arrangement 118 is provided for holding drum 72 infixed rotational position with a filter pair in the associated beampaths. Detent 118 comprises a series of five V-shaped notches120,122,124, 126 and 128 (FIG. 5) disposed about the periphery of drumdisc portion 82. Notches 120,122,124 and 126 are respectivelydiametrically opposed to filter pairs 84,92; 86,94;88,96; and 90,98.Notch 128 is for holding drum 72 in a rest position. A roller bearing130 is rotatably mounted in the plane of a drum axis 79 on aspring-biased pivot arm 132 for resiliently engaging the respectivedetents as drum 72 is rotated. Thus, in the position illustrated in FIG.5, bearing 130 resiliently engages notch 120 to hold fat reference andmeasurement filters 84,92 in reference and measurement beams 30,36 (FIG.1). When drum 72 is rotated to the next position wherein bearing 130engages notch 122, protein reference and measurement filters 86,94 areheld in the beam paths. Notch 124 operates in conjunction with lactosereference and measurement filters 88,96, and notch 126 operates inconjunction with water reference and measurement filters 90,98 in asimilar manner.

A program or code disc 112 (FIGS. 1 and 5) is mounted on gear 76 and isthereby rotatably coupled to filter drum 72 such that a peripheralportion of disc 112 passes through the optical sensor generallyindicated at 114 in FIG. 1 as a function of drum rotation. Opticalsensor 114 is responsive to peripheral apertures 116 (FIG. 5 andschematically in FIG. 3) in disc 112 for controlling system electronics(FIG. 3) to stop rotation of drum 72 when a selected filter pair isdisposed in the corresponding beams, to control the electronics formeasurement of the particular constituent with which the filter pair isassociated and to switch the pump motor on at the correct point in theoperation cycle. Provision of interference filter 24 adjacent infraredsource 20 (FIG. 1) for passing only a portion (three to ten microns) ofthe infrared spectrum of interest to the absorption-type reference andmeasurement filters reduces heating of the latter and improves accuracyof the overall apparatus.

A chopper shutter or disc 100 (FIGS. 1 and 6) is positioned at the zoneof intersection between reference beam 30 and measurement beam 36 at anorientation of 45° with respect to both beam axes. As best seen in FIG.1, disc 100 is angled to nest within the angle formed by drum rim anddisc portions 80,82. Disc 100 comprises a semicircular aperture 102(FIG. 6) and a semicircular reflective portion 104 alternatelypositioned in the paths of beams 30,36 at the point of intersectiontherebetween as disc 100 is rotated by the motor 106 coupled to the discdrive shaft 108 by the belt and pulley arrangement generally indicatedat 110 in FIG. 1. Thus, disc 100 nested within the rim and disc portionsof drum 72 is operative alternately to direct the measurement andreference beams through sample cell 66 onto detector 70. Morespecifically, when aperture 102 of disc 100 intersects the opticalbeams, reference beam 30 is transmitted on beam axis 34 through aperture102 and sample cell 66 to detector 70 while measurement beam 36 passesthrough the aperture away from the sample cell. When reflective discportion 104 intersects the respective beams, measurement beam 36 isfolded thereby to focus at sample cell 66 confocally with reference beam30, and thus is transmitted to detector 70 by ellipsoidal mirror 68. Atthe same time, reference beam 30 is reflected by the rear surface ofdisc portion 104 away from the sample cell.

Thus, rotation of disc 100 at the preferred frequency of 12.5 hertz (50hertz mains frequency) or 15 hertz (60 hertz mains frequency) operatesto transmit to detector 70 a composite beam which alternates inintensity as a function of the difference in percentage transmission ofa sample in cell 66 at the particular wavelengths transmitted bywhichever reference and measurement filters are in the beam paths.Detector 70 produces a signal which is amplified and conditioned byamplifier 111 and associated circuitry (FIG. 3) to drive servomotor 48(FIGS. 1 and 3). This positions comb 58 within beam 30 so as to minimizethis intensity differential. In this manner, the ultimate position ofthe servomotor 48, and the potentiometer coupled to it, for any filterpair, is proportional to the change in transmission of the samplesituated in cell 66 at the wavelengths transmitted by that filter pair.

FIG. 2 illustrates a presently preferred embodiment 140 of the fluiddrive system for placing test fluid in the sample cell generallyindicated at 66 in FIG. 1. System 140 comprises a diaphragm-typehomogenizer 142 (FIGS. 2 and 7) operatively coupled to an hydraulic pump144 (FIG. 2) and having an inlet 146 to draw a fluid milk sample fromthe vessel 149. Pump 144 includes a reciprocable piston 147 for drivinghydraulic fluid under pressure to homogenizer 142 through the conduit148. A code disc illustrated schematically at 150 in FIG. 2 is coupledto the piston drive mechanism (not shown) for cyclically operating pump144 in a manner to be described. A pressure relief valve 151, includinga valve stem 152 and a coil spring 154, is coupled internally of pump144 to conduit 148. In one working embodiment of the invention, pump 144comprises a Series (1) Actuator Pump marketed by Dia-meter Pumps Ltd. ofUnit 6, Fort Fareham Industrial Estate, Fareham, Hampshire, PO14 1AH.

Referring to FIGS. 2 and 7, homogenizer 142 includes a resilientdiaphragm 160 having an annular lip 161 captured between body blocks162,164. The central portion of diaphragm 160 is disposed within adiaphragm pump chamber 166. On one side of diaphragm 160, chamber 166 iscoupled by passage 168 extending axially through a fitting 169 to anipple 170 threadably received in fitting 169 for receiving hydraulicpump fluid through conduit 148 (FIG. 2). The other end 167 of fitting169 acts as a diaphragm stop on the decompression stroke of the pumpcycle. Fitting 169 is rigidly attached to block 164 and lip 171 takesthe axial load imparted on the compression stroke. An annular lip 165 inblock 162 insures accurate location of the diaphragm stop 167 inrelation to the diaphragm 160. High tensile bolts 163 are used to fastentogether blocks 162,164. A second passage 172 extends axially in block162 from chamber 166 through a gasket 174 and an orifice 176 to a firsthomogenizing valve generally indicated at 178.

Valve 178 comprises a sapphire ball 180 normally biased by a coil spring182 against a ceramic valve seat 184 restricting fluid communicationfrom diaphragm chamber 166. Valve 178 opens to a second homogenizingvalve 186 comprising a sapphire ball 190 biased by a coil spring 192against a stainless steel valve seat 194. Valve 186 opens to a nipple196. Nipple 196 is cemented into a fitting 195 which encloses spring 192and ball 190, and which in turn is threadably received into a largerfitting 193. Fitting 193 encloses orifice 176 and valve seats 184,194,all of which are held rigidly therein under compression by fitting 195in cooperation with a sleeve 191 surrounding ball 180 and spring 182.Fitting 193 is threadably received in block 162 and captures gasket 174in sealing engagement around the diaphragm-remote end of passage 172.

A passage 198 extends laterally of passage 172 to a gravity and pressureoperated check valve 200 comprising a ball 202 normally biased bygravity downwardly against a valve seat 204. A passage 206 extends fromvalve seat 204 to a nipple 205 for receiving a fluid sample throughconduit 146 (FIG. 2). Nipple 205 is cemented into a fitting 203 which,in turn, captures valve seat 204, ball 202 and a ball-guide sleeve 201within an outer fitting 199 by being threadably received in the latter.Fitting 199 is threadably received within block 162 in axial alignmentwith lateral passage 198 and captures a sealing gasket 197 therearound.Upward motion of ball 202 during suction of diaphragm 160 is limited bya pin 208 press fitted in and extending across sleeve 201.

Orifice 176 passes through a removable disc of stainless steel and isincluded in the homogenizer head merely as a means of enabling the partsto be disassembled. The valve seats, balls and springs may be removedfrom the separated homogenizer unit by first unscrewing fitting 195 fromfitting 193, and then pressing a rod against the disc containing thesmaller orifice 176 in a direction from right to left as shown in FIG.7.

In operation, pump 144 alternates between a negative or suction pressurewith reference to homogenizer 142 wherein diaphragm 160 is withdrawn tothe position illustrated in FIGS. 2 and 7, and fluid to be homogenizedand tested is drawn by negative pressure through conduit 146 and checkvalve 200 (FIG. 7) into chamber 166. On the next succeedingpressurization stroke, the diaphragm 160 is displaced to the left inFIGS. 2 and 7 forcing the sample fluid drawn during the suction portionof the pump cycle through orifice 176 and valves 178,186 to outletnipple 196. Preferably, the stroke of piston 147 (FIG. 2) is slightlygreater than the volume of diaphragm chamber 166 such that pressurerelief valve 151 (FIG. 2) is actuated on each stroke for deaerating thepump hydraulic fluid. Valve 151 preferably is set at 3800 psi. In thehomogenizer illustrated in FIGS. 2 and 7, a pump pressure in the rangeof 3000 to 5000 pounds per square inch, typically 3500 psi, iscontemplated. High pressure operation in this range and the two-stagehomogenizing valve arrangement 178,186, has been found to reduce theparticle size of the larger globules in whole milk to about two microns.

Sample cell 66 is illustrated schematically in FIG. 2 and in greaterdetail in FIGS. 8-13. Cell 66 comprises a pair of flat parallel opticalwindows 210,212 spaced from each other in assembly by a shim 214 ofcontrolled thickness and having an oval center opening for providing aplanar sample zone 216 between windows 210,212. In the preferredembodiment of the invention for measuring fat, protein, lactose andwater concentrations in milk, shim 214 and, therefore, planar samplezone 216 possess a thickness of thirty-seven microns. One of the windows210,212 is constructed of calcium fluoride material having a cut-off atapproximately 11 microns while the other window is of barium fluoridematerial having a cut-off at 12.5 to 13 microns. As best seen in FIGS. 8and 13, window 212 has a pair of circular openings 218,220 extendingtherethrough transversely of oval sample zone 216 and spaced from eachother lengthwise of the sample zone such that fluid entering opening218, which is an inlet opening, traverses the sample zone in the upwarddirection in FIG. 13 and then exists opening 220, which is the outletopening. Second openings 222,224 extend through outer window 210 inrespective alignment with inlet opening 218 and outlet opening 220, andcommunicate with a circular groove or channel 226 of semicircularsection having a preferred diameter of 0.3 mm formed on the face of astainless steel plate 228 cemented to window 210, such that a portion ofthe fluid entering inlet 218 will flow through opening 222, channel 226,opening 224 and then exit outlet 220 thereby to bypass sample zone 216.Plate 228 has an oval center opening 230 for admitting infraredradiation therethrough to windows 210,212.

Windows 210,212, shim 214 and plate 228 are placed in facing engagementas described. As best appreciated with reference to FIGS. 8 and 13, thissandwiched assembly is then located together with a centrally aperturedring 236 within the machined central bore 235 of a cylindrical block234. A pair of plates 232,233 having central openings of smalleraperture than bore 235 are then placed over the axial faces of cellblock 234 and fastened thereto by the pan head screws 231 and flat headscrews 239 to hold the sandwiched assembly within the cell block. Holesin 233 are counterbored to take springs 237 under the heads of screws231. Springs 237 serve to spring-load parts 236, 228, 210, 214 and 212together between plates 233 and 232 to give equal surface loading on allparts. Holes in plate 233 are large enough to allow heads of screws 238to pass therethrough and bed against the surface of block 234. Plate 232has openings 229 which align with openings 218,220 in window 212 andwhich receive sealing rings 227. The entire cell block assembly is thenfastened to a port block 240 by the screws 238.

Port block 240 includes inlet and outlet passages 242,244 (FIGS. 8, 10,12 and 13) respectively communicating with openings 218,220 in window212 through plate openings 229. Outlet passage 244 in block 240communicates through a tubular nipple 246 (FIGS. 9-11) and a conduit 248(FIG. 2) with a pressure valve 250 comprising a ball 252 biased by coilspring 254 to retard flow through conduit 248 (and therefore throughcell 66). Valve 250, when opened, feeds fluid in conduit 248 to wastethrough a drain 256. An inlet assembly 258 (FIGS. 9-12) comprises afitting 260 threadably received into a side opening in block 240 and ahollow tubular filter 262 extending axially from fitting 260 into acylindrical flow passage 264 in block 240. A passage 266 (FIGS. 11 and12) communicates transversely with passage 264 axially spaced fromfilter 262, and extends through block 240 to a second outlet nipple 268(FIGS. 9-11). Outlet nipple 268 is connected by a conduit 270 (FIG. 2)to a valve 272 controlled by disc 150 in pump 144. Nipples 246,268 arescrewed and cemented into associated openings in port block 240. As bestseen in FIG. 12, inlet passage 242 in block 240 communicates withpassage 264 at right angles approximately centrally of filter 262 suchthat fluid entering passage 242 passes through the filter side wall andis filtered thereby. A nipple 259 is a running fit into fitting 260 forconnection to conduit 197 (FIG. 2) from homogenizer 142.

Thus, it will be evident that, with pressure valve 250 (FIG. 2) normallyclosed and control valve 272 held normally open, fluid fed to samplecell inlet 258 by homogenizer 142 normally flows through the hollowcentral opening in filter 262, through passages 264,266, nipple 268(FIGS. 11 and 12), conduit 270 (FIG. 2) and valve 272 to waste, wherebyfilter 262 is self-cleaning. On the other hand, when valve 272 isclosed, fluid pulses from homogenizer 142 are routed through the sidewall of filter 262 into passage 242 (FIGS. 2, 10 and 12-13) in block240. A portion of this fluid passes through sample zone 216 while theremainder bypasses the sample space through channel 226 (FIG. 13) inplate 228 as previously described. Disc 150 (FIG. 2) controls pump 144such that each sampling cycle comprises a plurality of between five andfifteen, preferably twelve, pulsations of homogenizer 142. On the firsteleven pulsations in the preferred mode of operation, valve 272 is heldopen such that the homogenized milk effectively purges homogenizer 142,conduit 197 and inlet assembly 258. In particular, it will beappreciated that the purging fluid tends to wash tubular filter 262.Prior to the twelfth pulsation of homogenizer 142, valve 272 (FIG. 2) isclosed. Thus, the pressure of the twelfth pulsation is effective to openpressure valve 250 such that fluid is then routed through the side wallof tubular filter 262 and through sample zone 216 as previouslydescribed. After the twelfth pulsation, operation of pump 144 isautomatically terminated by disc 150 (FIG. 2) and opticalcharacteristics of the sample in sample zone 216 may be measured.

Preferably, each pulsation of homogenizer 242 provides approximately 0.6milliliters of homogenized fluid. The sample zone 216 itself holdsapproximately 0.005 milliliters of fluid. Thus, it will be appreciatedthat the total volume of fluid provided by homogenizer 142 during eachpurging and cell-refill cycle, and also during the twelfth pulsationthrough the sample zone itself, is substantially in excess of thatrequired for obtaining a measurement sample. However, the additionalwastage offers the significant advantage previously described ofautomatically purging all flow lines including the cell. Preferably,conduits 197,270 and 248 (FIG. 2) are constructed of resilient materialsuch as tubular PVC for elastically absorbing transient pressures causedby the pulsating fluid flow thereby to prevent flexure of opticalwindows 210,212.

Plates 228, 233, 232, cell block 234, ring 236 and port block 240 (FIG.8) are preferably constructed of corrosion resistant material such asstainless steel. Heating resistors 274,276 are mounted on thecell-remote side of block 240 and are connected to appropriate controlcircuits 278 (FIG. 3) for heating block 240 and thereby maintaining thetemperature of sample cell assembly 66 at a selected temperature aboveinstrument temperature. For analysis of milk, a cell temperature of40°±0.2° C. is preferred. Temperature control circuit 278 may comprise asuitable bridge circuit or the like responsive to a thermistor 280(FIGS. 3 and 11) mounted on the port block assembly 240. Similartemperature control structure is preferred in connection withhomogenizer 142 but is not illustrated in FIG. 7. Preferably,homogenizer 142 is physically located closely adjacent to cell 66 butexternal to the optics unit, and test measurements are performed a shorttime after fluid sample is placed in the cell so that the homogenizedfat particles in the milk do not have an opportunity to form aggregates.

Instrument measuring and control circuits are illustrated in functionalblock form in FIG. 3 and include decoding circuitry 282 responsive tocoded apertures 116 in program disc 112 through optical sensor 114 forindicating which of the filter pair on drum 72 is in the beam paths, andthereby controlling the remainder of the circuits for measurement offat, protein, lactose and water/solids concentrations. Detector 70 isconnected through the normally closed contacts of a run/calibrate switch284 to the input of amplifier 111, which is a.c. coupled and tuned to12.5±3 Hz (for 50 hertz line frequency) or to 15±3 Hz (for 60 hertz linefrequency). Connection of detector 70 to amplifier 111 is through one offour variable resistors 450-456 (selected through switches 460-466 byphotoposition decoding circuitry 282 for fat, protein, lactose andwater/solids respectively) which determines the servo amplifier voltagegain and hence sensitivity to the detector signal voltage for eachcomponent being measured. The amplifier output drives servomotor 48which controls the comb position.

A voltage derived from the potentiometer 468 coupled to the combmechanism provides velocity feedback to amplifier 111 insuring acontrolled rate of comb movement. Also coupled to the comb mechanism isthe precision potentiometer 290. Thus, a voltage directly proportionalto comb position is provided to an input of amplifier 470. Summed tothis amplifier is a voltage derived from one of four preset adjustableresistors 472-478 selected through switches 480-486 by photopositiondecoding circuitry 282 for fat, protein, lactose and water/solidsrespectively. This provides a bias to the comb position voltage prior tologging by log amplifier 292. Adjustment of the bias allows the outputof the log amplifier 292 to be linear for equal increments of %T of thecomponent being measured in the cell in accordance with Beer's law.Beer's law is: D=ln 1/T for D equals optical density, T equals percenttransmission and ln indicates the taking of the natural logarithm (basee).

The sequential concentration signals from log amplifier 292 are fed byslope control resistors 294-300 through switches 302-308 controlled bydisc decode circuitry 282 to a four-channel memory, correction andscaling circuit 310 which will be described in greater detail inconnection with FIG. 14. Circuit 310 provides at its output a series ofuncorrected signals F_(o),P_(o),L_(o) and W_(o) for fat, protein,lactose and water respectively, and a second series of signals F, P, Land W/S which have been cross-corrected for effects due to change inabsorption of infrared energy at the particular test wavelengthsselected for the others. The outputs of circuit 310 are connectedthrough a four-pole double-throw switch generally indicated at 312 forselecting either corrected or uncorrected signals, and through afour-channel a/d converter 314 to digital readouts 316,318,320 and 322for indicating concentration in percentage by weight of fat, protein,lactose and water or solids respectively. Displays 316-322 preferablycomprise decimal displays.

The decoded outputs of circuit 282 are additionally connected to anoptical zero adjustment circuit 324 which controls the position of vane40 (FIG. 1) by means of motor 42. Zero adjust circuit 324 receivessecond control inputs from the manually adjustable resistors 326,328,330and 332 for placing vane 40 (FIG. 1) in the desired zero adjustmentposition for fat, protein, lactose and water respectively. Calibrationof zero adjustment circuit 324 and of memory, correction and scalingcircuit 310 will be discussed in greater detail hereinafter. It will beappreciated, of course, that the various resistors illustrated in FIG. 3(and in FIG. 14 yet to be described) are to be connected to appropriatebiasing voltages such as +12 volts, -12 volts and zero volts.

Referring now to FIGS. 14a-14c, memory correction and scaling circuitry310 illustrated therein basically comprises four circuit channels340,346,348 and 350 (FIGS. 14a-14b) respectively labeled for providingcorrected and uncorrected indications of fat, protein, lactose and waterconcentrations, and a fifth channel 432 (FIG. 14c) for deriving anindication of non-fat solid concentration or total solid concentrationfrom signals available in the other four channels. Fat channel 340receives an input signal from adjustable scaling resistor 294 (FIGS. 3and 14a) through switch 302, which preferably comprises an FET switchcontrolled by disc decode electronics 282 as previously described. Theswitched input signal is fed and stored on a capacitor 342 across theinput of a high impedance input current amplifier 344 which provides atits output the uncalibrated fat signal F_(o). Similarly, protein,lactose and water channels 346,348 and 350 each include a correspondingstorage capacitor 352,354 and 356 connected across the input of the highimpedance input amplifiers 358,360 and 362 for providing uncorrectedprotein, lactose and water signals P_(o),L_(o) and W_(o) respectively.

The output of fat input amplifier 344 is connected in fat channel 340through an adjustable resistor 364 to a summing junction 366 at theinput of second stage amplifier 368. The output of amplifier 344 is alsoconnected through the adjustable resistors 370 and 372 to the summingjunctions 376 and 378 at the inputs of second stage amplifiers 382 and384 in protein and lactose channels 346 and 348, and through theadjustable resistor 374 to one input of the second stage amplifier 386in water channel 350. The output of protein input amplifier 358 isconnected through an adjustable resistor 388 to protein summing junction376, through a second adjustable resistor 390 to fat summing junction366, and through a third adjustable resistor 391 to lactose summingjunction 378. The output of lactose input amplifier 360 is connectedthrough a first adjustable resistor 394 to lactose summing junction 378,through a second adjustable resistor 396 to protein summing junction376, and through a third adjustable resistor 398 to fat summing junction366. The output of water input amplifier 362 is fed to a summingjunction 380 at a second input of second stage amplifier 386, the outputof which is connected to fat summing junction 366 through the adjustableresistor 400, to protein summing junction 376 through adjustableresistor 402 and to lactose summing junction 378 through the adjustableresistor 404. Summing junctions 366,376,378 and 380 are additionallyconnected to the adjustable resistors 406,408,410 and 412 respectively.

Second stage amplifier 368 in fat channel 340 is connected through anoutput amplifier 414 for providing an analog signal (voltage) F as alinear function of fat concentration and corrected for cross-absorptioneffects as previously described. Similarly, protein and lactose secondstage amplifiers 382 and 384 are connected through corresponding outputamplifiers 416 and 418 for providing corrected analog protein andlactose signal (voltages) P and L. The output of amplifier 386 in waterchannel 350 is connected through an output amplifier 420 to oneselectable contact of a switch 422 which selects either waterconcentration W or one of the solid concentrations TS (total solids) orSNF (solids non-fat) for display on digital readout 322 (FIG. 3). Theoutput of second stage amplifier 368 in fat channel 340 is additionallyconnected to solid channel 432 through the adjustable resistors 426 and428 to the two selectable contacts of a switch 430 for choosing TS orSNF for display. The common contact of switch 430 is connected to asumming junction 434 at the input of an amplifier 436. The output ofsecond stage amplifier 382 in protein channel 346 is connected throughan adjustable resistor 438 to solid summing junction 434. The output oflactose second stage amplifier 384 is connected through the adjustableresistor 440 to junction 434, and the output of water second stageamplifier 386 is connected through an adjustable resistor 442 (FIG. 14b)to summing junction 434. An adjustable resistor 444 provides an offsetvoltage to compensate in the solids and solids non-fat readout for theaverage value of mineral matter in milk. The wipers of adjustableresistors 370,372 and 374 in fat channel 340,390 and 392 in proteinchannel 346,396 and 398 in lactose channel 348, and 400,402,442 and 404in water channel 350 have normally open switches connected thereacrossto ground for short circuiting the respective adjustable resistorsduring the calibration operation to be described.

Corrected signals for fat F, protein P, lactose L, water W, total solidsTS and solids non-fat SNF are given by the following equations:

    F=aF.sub.o +bP.sub.o +cL.sub.o +dW+e

    P=fF.sub.o +gP.sub.o +hL.sub.o +iW+j

    L=kF.sub.o +mP.sub.o +nL.sub.o +oW+p

    W=W.sub.o +qF.sub.o +r

    TS=sF+tP+uL+xW+v

    SNF=wF+tP+uL+xW+v

wherein the coefficients a-x are predetermined empirically and areadjusted by the variable resistors in FIGS. 14a-14c.

    ______________________________________                                                         calibrated by                                                coefficient      variable resistor                                            ______________________________________                                        a                364                                                          b                390                                                          c                398                                                          d                400                                                          e                406                                                          f                370                                                          g                388                                                          h                396                                                          i                402                                                          j                408                                                          k                372                                                          m                392                                                          n                394                                                          o                404                                                          p                410                                                          q                374                                                          r                412                                                          s                428                                                          t                438                                                          u                440                                                          v                444                                                          w                426                                                          x                442                                                          ______________________________________                                    

The values of coefficients a-x depend upon the characteristics of thefilters and vary a great deal from one filter batch to another.

Before discussing overall operation of the invention, the method ofcalibration will be briefly described. First, referring to FIGS. 1-3,pump 144 is operated to draw water, preferably distilled water, intohomogenizer 142 and pulse water through the fluid system to purge thehomogenizer, the various conduits and sample cell 66. A "sample" ofwater is left in the sample cell. Servomotor 48 is turned on and switch312 (FIG. 3) is in the uncorrected position. Filter drum 72 (FIG. 1) isthen operated sequentially to place the fat, protein, lactose and waterfilter pairs in the respective optical beams. With the fat filters inthe beams, for example, and chopper 100 energized such that radiation isincident on detector 70 as an alternating function of the intensity ofthe sample and reference beam passing through the sample cell, resistor326 (FIG. 3) is adjusted until the arcuate comb 58 is in an arbitrary"zero" position which yields a "zero" reading at display 316. Asresistor 326 is adjusted, vane 40 (FIG. 1) is correspondingly adjustedto selectively attenuate measurement beam 36 so that the measurement andreference beams at 3.418 and 3.47 micron wavelength respectively areequal in intensity at detector 70. This procedure is then repeated forprotein, lactose and water successively, such that resistors 328,330 and332 (FIG. 3) are adjusted to correspond to zero positions for each ofthese measurements respectively. Thereafter during measurementoperations, optical zero adjust circuitry 324 (FIG. 3) willautomatically rotate vane 40 by means of motor 42 to the adjusted zeroposition depending upon the constituent to be measured.

With switches 430 and 422 (FIG. 14c) in the TS or total solids position,servomotor 48 (FIG. 3) is disconnected (by switch means not shown) andresistor 444 (FIG. 14c) is adjusted until the reading on display 322(FIG. 3) is equal to the sum of displays 316,318 and 320. With servo 48off, filter drum 72 is then rotated to the fat position and resistor 294(FIGS. 3 and 14a) is adjusted while switch 312 is sequentially switchedback and forth between corrected and uncorrected positions until thecorrected and uncorrected fat signals indicated at readout 316 areidentical. The same procedure is then repeated for protein, lactose andwater such that adjustable resistors 294-300 are in their calibratedpositions.

Drum 72 is then again returned to the fat position and switch 284 (FIG.3) is placed in the calibrate position wherein servo amplifier 286 isconnected to adjustable resistor 288. Servomotor 48 is re-energized andresistor 288 is adjusted until digital display 316 reads "10.00" withswitch 312 in the uncorrected position. The switches across adjustableresistors 370,372 (FIG. 14a) are open and the remaining switches acrossthe various adjustable resistors in FIG. 14 are closed. Resistors364,370 and 372 are then adjusted while switch 312 (FIG. 3) isalternately switched between corrected and uncorrected positions untilthe corrected fat signal equals 10a, i.e. aF_(o), the corrected proteinsignal equals the uncorrected P signal (P_(o)) plus 10f and thecorrected lactose signal equals the uncorrected signal L_(o) plus 10k.Filter drum 72 (FIG. 1) is then moved to the protein position andresistor 288 is adjusted to yield an uncorrected signal P_(o) on display318 of "10.00". The switches across adjustable resistors 390,392 (FIG.14a) are opened and the remaining resistor-bridging switches in FIG. 14are closed. Resistors 388,390 and 392 are then adjusted while switch 312(FIG. 3) is alternately switched between corrected and uncorrectedpositions until the corrected protein signal on display 318 is equal to10g, i.e. gP_(o), the corrected fat signal at display 316 is equal tothe display at the uncorrected position of switch 312 plus 10b and thecorrected lactose signal at display 320 is equal to the signal in theuncorrected position of switch 312 plus 10m. Drum 72 is then rotated tothe lactose position and resistor 288 is adjusted to yield anuncorrected lactose signal at display 320 of "10.00". The switchesbridging resistors 396 and 398 (FIG. 14b) are opened and the remainingresistor-bridging switches in FIG. 14 are closed. Resistors 394,396 and398 are then adjusted while switch 312 (FIG. 3) is alternately switchedbetween corrected and uncorrected positions until the corrected lactosesignal at display 320 is equal to 10n, the corrected fat signal atdisplay 316 is equal to the signal when switch 312 is in the uncorrectedposition plus 10c and the corrected protein signal at display 318 isequal to the signal when switch 312 is in the uncorrected position plus10h. Servomotor 48 is then turned off. All resistor-bridging switches inFIG. 14 are closed and switch 312 is placed in the uncorrected position.Resistor 444 (FIG. 14c) is then re-adjusted until the display at 322 isequal to the sum of the displays at 316-320 plus the required correctionconstant v.

For normal application to the analysis of whole milk for fat, protein,lactose and solids or solids non-fat, circuits 340,346,348 and 432 willnormally be used. Up to now it has not been found necessary to applywater corrections to the fat, protein, or lactose channels. At the timeof determining the design features of the invention described herein, itwas visualized that the water channel could be employed in the followingways.

(1) As an extra means of applying cross corrections to fat, protein,lactose channels and thus indirectly to solid channel for variation inmineral matter. This has not proven to be worthwhile, presumably becausethe mineral matter being of high specific gravity, or small bulk,displaces little water and therefore shows little sensitivity to changein content of mineral matter. The means for applying these correctionsare still available and the coefficients are adjusted in the same way asdescribed for fat, protein and lactose but using resistors400,402,404,442.

(2) As a direct means of determining total solids or solids non-fat.This is effected by measuring at the water wavelengths the displacementof water by other components and relating this directly to resultsobtained from standard methods (e.g. gravimetric and hydrometer).Results compared by these two methods (instrument v. either standard)have given standard deviations of 0.1%. However, standard deviations aslow as 0.07-0.08% are easily achieved using the summation method and, todate, this latter method has been preferred. Note: when this directmethod is used for solids non-fat, the effect of fat is offset byswitching into use resistors 374 in the fat channel 340.

(3) As a means of applying total corrections to individual components.Each component can be corrected for effects of all other components byusing water-only corrections, e.g. equally accurate results have beenachieved for fat using water correction as with the protein and lactosecorrections applied separately.

An instrument user requiring fat-only readout could therefore obtain afaster rate of sampling using the fat/water correction combination.Also, in cases where fat and solids non-fat or fat and total solidsresults are required by the user who is able to tolerate slightly lessaccurate solids measurements, this method would be preferred. It shouldbe explained that in order to obtain corrections for displacement ratherthan absorption effects, the infrared filters are reversed in theoptical system, i.e. the water absorption filter is placed in thereference beam and the reference filter is placed in the measuring beam.There is no doubt that for some milk product analysis applications thewater channel will be used to good effect.

Constants e, j, p and r are not required when the instrument is set upfor analysis of whole milk. It is, however, visualized that for certainapplications to milk product analysis, it may be necessary to include anintercept adjustment. In such cases this can be effected in fat,protein, lactose and water channels by adjustments to resistors406,408,410 and 412. The value of these constants or intercepts will beindicated by the calibration data for the appropriate component.

With all adjustments made, the embodiment of the invention hereinabovedescribed is now ready for operation. Referring to FIGS. 1-4, a specimenof milk to be sampled as in cup 149 in FIG. 2 is located beneathhomogenizer inlet tube 146. Pump 144 is then activated to provide elevenpulses of milk from the specimen through homogenizer 142 to purge thesample cell 66 and the lines connecting the homogenizer to the samplecell. After the twelfth pulse from homogenizer 142, which places aspecimen to be tested within the sample cell, pump operation isautomatically terminated. Filter drum 72 is then activated sequentiallyto stop at the fat, protein, lactose and water positions. In the fatposition, reference and measurement beams are alternately directedthrough the sample cell 66 onto the detector 70 which, in turn, operatesservomotor 48 to position comb 60 within reference beam 30 (FIG. 1)until the reference and measurement beams seen by the photocell areequal in intensity. The signal on resistor 290 (FIG. 3) indicative offat concentration is then stored on capacitor 342 (FIG. 14a). Thisprocess is repeated in the protein, lactose and water positions offilter drum 72. Corrected fat, protein and lactose concentrations inpercent are then displayed at 316-320. If water display is desired,switch 422 (FIG. 14c) is placed in the position indicated and percentwater concentration is displayed at 322. If total solids or solidsnon-fat are desired, switch 422 is placed in the alternative positionand switch 430 is placed in the desired position such that percentage oftotal solids or solids non-fat is automatically provided at display 322.The specimen at 149 may then be changed and the cycle repeated asdesired.

The invention claimed is:
 1. Apparatus for quantitative analysis ofoptical characteristics of fluent materials comprising a source ofradiation in the infrared spectrum, first means for splitting radiationfrom said source into first and second convergent beams, a drum disposedto rotate about a fixed axis and having a circumferential rim portiondisposed to intersect one of said beams as said drum is rotated and anaxial disc portion disposed to intersect the other of said beams as saiddrum is rotated, an optically transparent cell aligned with said firstbeam for holding a test sample, chopper means disposed between said drumand said cell and adapted to alternate between a first position in whichsaid first beam is directed through said cell and a second position inwhich said second beam is directed through said cell, optical filtermeans disposed in said disc and rim portions of said drum as tointersect respective ones of said beams such that said chopper meansalternately directs first and second beams through said cell atwavelengths corresponding to said filter means in said first and secondpositions of said chopper means, and energy responsive means disposed tobe responsive to radiation transmitted through said cell for indicatingan optical characteristic of a test sample within said cell.
 2. Theapparatus set forth in claim 1 wherein said rim is substantiallycylindrical and said disc portion is perpendicular to said rim portion,and wherein said first and second beams are orthogonally convergentafter passage through said filter means.
 3. The apparatus set forth inclaim 2 wherein said cell is disposed on axis with one of said first andsecond beams, and wherein said chopper means comprises a rotatable discdisposed at the zone of intersection of said first and second beams andhaving a first transparent circumferential portion for passing saidfirst beam to said cell and a second reflective circumferential portionangulated to reflect the other of said first and second beams on axis tosaid cell.
 4. The apparatus set forth in claim 3 wherein said filtermeans comprise first and second series of optical filters respectivelydisposed in said rim and disc portions of said drum with filters in saidfirst and second series being grouped in coordinated pairs on radii fromthe radiation axis of said drum such that filters in said pairssimultaneously intersect associated ones of said first and second beams.5. The apparatus set forth in claim 4 for quantitative analysis of amultiplicity of optical characteristics of a test sample contained insaid cell, each said filter pair comprising a reference filter and ameasurement filter for passing light to said cell at differingpreselected wavelengths such that one of said characteristics ismanifested by a difference in energy absorption at said differingwavelengths, wherein said light responsive means includes circuit meansresponsive to said difference in energy absorption for measuring saidone characteristic.
 6. The apparatus set forth in claim 5 furthercomprising means for step-wise rotation of said drum for locating eachof said filter pairs in said beam, said circuit means being responsiveto differences in energy absorption at the said differing wavelengths ofeach said filter pair for measuring each said characteristic, andcontrol means coupled to said drum for controlling said circuit means asa function of the filter pair intersecting said beams.
 7. The apparatusset forth in claim 6 further comprising adjustable first energy shuttermeans disposed to intersect one of said beams, and means coupled to saidcontrol means for adjustably positioning said first shutter means withinsaid one beam at a position selected for each said filter pair toprovide a zero indication of optical characteristics at said radiationresponsive means in the absence of a sample in said cell.
 8. Theapparatus set forth in claim 6 wherein said filter means comprises firstand second series of absorption filters each selected to transmitradiation in a band around a selected nominal peak wavelength, saidfirst and second series being adapted to transmit wavelengths in aselected range of the infrared spectrum, and wherein said radiationsource includes interference filter means for transmitting to saidabsorption filters substantially only energy within said range so as tominimize heating of said absorption filters.
 9. The apparatus set forthin claim 6 for measuring fat, protein and lactose concentrations in milkwherein said reference and measurement filters are grouped in pairshaving respective nominal peak transmission wavelengths of about 3.47μand 3.418μ for fat, 6.68μ and 6.46μ for protein, and 7.67μ and 9.6μ forlactose.
 10. The apparatus set forth in claim 9 for further measuringwater concentration in milk wherein said reference and measurementfilters are grouped in an additional pair possessing respective nominalpeak transmission wavelengths of about 5.55μ and 4.7μ for measurement ofwater concentration.
 11. In an apparatus for quantitative analysis ofoptical characteristics of materials comprising an infrared source, anoptically transparent cell for holding a test sample, means forsplitting energy from said source into first and second beams, means foralternately directing said first and second beams through said cell,energy responsive means disposed to receive radiation transmittedthrough said cell alternately in said first and second beams, andradiation filter means disposed to intersect said first and second beamssuch that radiation incident on said energy responsive means in saidfirst and second beams exhibit differing wavelength characteristics, theimprovement wherein said beam splitting means comprises means forsplitting said beam into a said first beam on a first axis whichintersects said cell and energy responsive means, and a said second beamon a second axis orthogonally intersecting said first axis, wherein saidfilter means comprises rotatable means having first and second series offilters disposed in orthogonal pairs and means for stepwise rotation ofsaid rotatable means such that selected ones of said first and secondfilter series comprising said pairs are alternately positioned tointersect said first and second beams, and wherein said means foralternately directing said beams through said cell comprises a chopperhaving a transparent portion and a reflective portion, means positioningsaid chopper at the area of intersection of said first and second axesat an orientation of 45° with respect to both said axes, and means forrotating said chopper such that, in alternation, said first beam istransmitted by said transparent portion to said cell and said secondbeam is reflected by said second portion to said cell.
 12. The apparatusset forth in claim 11 wherein said first and second beams aresubstantially confocal at said cell.
 13. The apparatus set forth inclaim 12 wherein said beam splitting means comprise first and secondplane mirrors reflecting light from said source, a first sphericalmirror disposed to receive said first beam from said first plane mirrorand to focus said first beam at said cell, and a second spherical mirrordisposed to receive said second beam from said second plane mirror andto cooperate with said reflective position of said disc to focus saidsecond beam at said cell, and wherein said apparatus further comprisesan ellipsoidal mirror having a first focus at said cell and a secondfocus at said light responsive means.
 14. The apparatus set forth inclaim 11 wherein said energy responsive means comprises thermoelectricmeans disposed such that first and second beams are alternately incidentthereon, shutter means adapted to be adjustably positioned in one ofsaid first and second beams, servo means coupled to said thermoelectricmeans and responsive to differing intensity of said first and secondbeams alternately incident on said thermoelectric means for adjustablypositioning said shutter means in said one of said beams until saidintensities are equal, and means responsive to said servo means forindicating said optical characteristics.
 15. The apparatus set forth inclaim 14 wherein said servo means comprises a pivot arm carrying saidshutter means, a servo motor electrically connected to said lightresponsive means, transmission means coupling said pivot arm to saidmotor, and a coil spring coupled to said pivot arm for biasing saidpivot arm and said transmission means against said motor such that saidmotor exhibits substantially zero backlash.
 16. Apparatus forspectrophotometric absorption analysis of material comprising a sourceof infrared radiation means including means for generating first andsecond divergent beams from said source, a cell for holding a testsample of material, first reflective means disposed in the path of saidfirst beam for focusing said first beam at said cell on an optical axis,detection means, ellipsoidal reflective means having a first focus atsaid cell and a second focus at said detection means, second reflectivemeans disposed in the path of said second beam for redirecting saidsecond beam to intersect said first beam orthogonally to said axis andto focus said second beam, means disposed at the zone of intersection ofsaid first and second beams for alternately and sequentially directingsaid first and second beams through said cell such that said second beamis substantially confocal with said first beam when directed throughsaid cell, filter means having a first portion disposed to intersectsaid first beam between said first reflective means and said means foralternately directing said beams through said cell, a second portionorthogonal to said first portion and disposed to intersect said secondbeam between said second reflective means and said means for alternatelydirecting said beams, first and second series of optical filtersrespectively disposed on said first and second portions in coordinatedpairs such that filters in said pairs simultaneously intersect saidfirst and second beams and means for alternately locating selected oneof said filter pairs in said beams, and means coupled to said detectionmeans and responsive to differing intensity of beams passing througheach said filter pair and through said cell for measuring opticalcharacteristics of the test sample.
 17. Apparatus for opticallyanalyzing fluid emulsions such as milk which comprises an opticallytransparent cell for holding a sample of said emulsion of predeterminedquantity, means including a homogenizer having an inlet to receive saidfluid emulsion and an outlet for providing a quantity of homogenizedfluid substantially in excess of said predetermined quantity, firstconduit means for directing fluid from said homogenizer through saidsample cell, second conduit means operatively connected to said firstconduit means upstream of said cell for routing fluid to bypass saidcell, control means coupled to said homogenizer means, said firstconduit means and said second conduit means for directing a firstmeasured quantity of homogenized fluid through said first conduit meansand said second conduit means bypassing said cell so as to purge saidhomogenizer and said first conduit means and then for directing a secondmeasured quantity of homogenized fluid through said first conduit meansto said cell, and means responsive to said control means for directingan optical beam through said cell so as to analyze fluid in said cellfor a selected optical characteristic.
 18. The apparatus set forth inclaim 17 wherein said control means comprises a first control valvedisposed in one of said first and second conduit means and operate whenopen to permit passage of fluid through the associated said conduitmeans, and means for closing said control valve for directing fluidthrough the other of said conduit means.
 19. The apparatus set forth inclaim 18 wherein said control means further comprises a second controlvalve disposed in the said other of said conduit means, said secondcontrol valve including means normally closing said second control valveso as to resist passage of said fluid through said other conduit meanswhen said first control valve is open and means responsive to increasein pressure in said other conduit means when said first control valve isclosed to open said second control valve.
 20. The apparatus set forth inclaim 19 wherein said homogenizer includes two valves and a hydraulicdiaphragm pump for receiving and directing fluid emulsion through saidvalves, wherein said means including said homogenizer includes means forproviding pulsed hydraulic energy to said diaphragm pump such that saidquantity of fluid appears in pulses, and wherein said control meansfurther comprises means coupled to said pulsed hydraulic energyproviding means and to said first control valve for directing a seriesof first pulses through said first and second means bypassing said cellfor purging said first conduit means and a series of second pulsesthrough said first conduit means both to purge said cell and to fillsaid cell with filtered fluid to be analyzed.
 21. The apparatus setforth in claim 20 wherein said cell comprises a pair of opposed windowsseparated by a space for holding test material, and wherein said firstand second conduit means are of resilient tubular construction forelastically absorbing impulse fluid pressure from said homogenizer andthereby preventing flexure of said cell windows.
 22. The apparatus setforth in claim 21 wherein said second series of pulses comprises onepulse of emulsion substantially in excess of that needed to fill saidcell.
 23. The apparatus set forth in claim 22 for analyzing milk furthercomprising means mounted to said homogenizer for heating saidhomogenizer to a temperature above room temperature.
 24. The apparatusset forth in claim 23 wherein said temperature is substantially 40° C.25. The apparatus set forth in claim 17 further comprising filter meansdisposed at the junction of said first and second conduit means, suchthat said second measured quantity of fluid flowing through said firstconduit means to said cell passes through and is filtered by said filtermeans, while said first measured quantity of fluid flowing through saidfirst and second conduit means bypasses and tends to wash said filtermeans.
 26. The apparatus set forth in claim 17 wherein said sample cellcomprises a pair of flat parallel optical windows and means spacing saidwindows from each other to provide a generally planar sample zone, fluidinlet and outlet ports including openings extending through one of saidwindows and spaced from each other such that fluid entering said inletport traverses said zone between said windows before exiting said outletport, a fluid passage extending past said inlet port and connecting withsaid inlet port through an opening in a side wall of said passage, and afilter medium carried against said passage side wall across said openingsuch that fluid which enters said zone through said inlet port isfiltered by said filter medium while fluid passing through said passagepast said inlet port tends to wash said filter medium.
 27. The apparatusset forth in claim 26 wherein said cell further comprises a plate havinga flat surface carried in facing engagement with the other of saidwindows externally of said zone, passages extending through said otherwindow and opening into said zone, and a groove in said flat platesurface in fluid communication with said passages in said other windowsuch that a quantity of fluid entering said zone through said inlet portbypasses said zone by passing through said passages in said other windowand through said groove.
 28. The apparatus set forth in claim 27 whereinsaid plate has a central opening for passage of an optical beam throughsaid windows, wherein said groove is generally circular surrounding saidopening in said plate, and wherein said passages in said other windoware substantially aligned with said openings extending through said onewindow.